We investigated the Dirac-cone state and its modulation when an ultrathin film of topological insulator Bi${}_2$Se${}_3$ was epitaxially grown on a van-der-Waals ferromagnet Cr${}_2$Si${}_2$Te${}_6$ (CST) by angle-resolved photoemission spectroscopy. We observed a gapless Dirac-cone surface state in 6 quintuple-layer (QL) Bi${}_2$Se${}_3$ on CST, whereas the Dirac cone exhibits a gap of 0.37 eV in 2QL counterpart. Intriguingly, this gap is much larger than those for Bi${}_2$Se${}_3$ films on Si(111). We also revealed no discernible change in the gap magnitude across the ferromagnetic transition of CST, suggesting the very small characteristic length and energy scale of the magnetic proximity effect. The present results suggest a crucial role of interfacial coupling for modulating Dirac electrons in topological-insulator hybrids.

中文翻译：

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范德华铁磁体Cr2Si2Te6上外延Bi2Se3ultrathin薄膜中Dirac电子的调制

我们研究了拓扑绝缘子Bi的超薄膜时的狄拉克锥状态及其调制${}_2$硒${}_3$ 在Van-der-Waals铁磁体Cr上外延生长${}_2$硅${}_2$特${}_6$（CST）的角度分辨光发射光谱。我们在6层五层（QL）Bi中观察到了无间隙的狄拉克锥表面状态${}_2$硒${}_3$在CST上，而Dirac锥在2QL对应物上的间隙为0.37 eV。有趣的是，这个差距比Bi的差距大得多${}_2$硒${}_3$Si（111）上的薄膜。我们还发现，在CST的铁磁跃迁上，缝隙大小没有明显变化，表明磁邻近效应的特征长度和能级很小。目前的结果表明界面耦合对于调制拓扑绝缘子杂化中的狄拉克电子具有至关重要的作用。